Electrochemical device and method for scale deposition and removal

ABSTRACT

An electrochemical device for scale treatment in water supply systems, having: (a) an electrochemical cell including: (i) a metallic tank for receiving a water supply, the tank forming a cathode of the electrochemical cell; and (ii) at least one anode, disposed within the tank; the electrochemical cell being operative to produce a pH above 12 near a wall of the tank, so as to form a scale deposition on the wall, thereby removing the deposition from the water supply; (b) an elastic scraper disposed for scraping the inner wall of the tank, and (c) a control system for the elastic scraper, designed and configured to activate the scraper so as to promote the deposition of scale on the wall.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to an electrochemical system for removingscale from water supply systems, and, in particular, to anelectrochemical system having a scale-removing scraper for removingscale from the cathode surface so as to increase the rate of scaledeposition thereon.

Various systems are known for preventing scale precipitation anddeposition in both hot and cold water systems. Substantially, thesesystems prevent the deleterious deposition and build-up of scale byprecipitating the hardness in the water, so as to produce a suspendedcolloid. Systems known in the art utilize, inter alia, ultrasonic,magnetic, electrostatic, catalytic, and electrochemical means to reducethe undesirable precipitation of scale.

Among the known electrochemical devices are the modern and efficientsystems based on the “Guldager” electrolytic method. In these systems,aluminum anodes, connected to an external electrical supply source, areimmersed in metallic water tanks. The anodes are oxidized by the water,while the water becomes alkaline with high pH values close to the innerwall of the tank, precipitating calcium carbonate (CaCO₃) and dissolvingthe aluminum anodes in the water as aluminum hydroxide [Al(OH)₃].

In my Israeli Patent No. 120,003 is disclosed a modified Guldager systemhaving non-dissolving electrodes made of, or coated with, a TiNiO alloy.In this system, which will be described in greater detail hereinbelow,the scale is deposited on the inner wall of the tank, and is removed bya scraping action against the wall.

It would be highly advantageous to have an improved method of, and adevice for, electrochemically treating water supply systems that wouldfurther reduce the water hardness (i.e., the level of unprecipitatedscale) in such systems. It would be of further advantage if the improvedmethod and device would be simple, robust, and inexpensive.

SUMMARY OF THE INVENTION

According to the teaching of the present invention there is provided anelectrochemical device for scale treatment in water supply systems,having (a) an electrochemical cell including: (i) a metallic tank forreceiving a water supply, the tank forming a cathode of theelectrochemical cell; and (ii) at least one anode, disposed within thetank; the electrochemical cell being operative to produce a pH above 12near a wall of the tank, so as to form a scale deposition on the wall,thereby removing the deposition firm the water supply; (b) an elasticscraper disposed within the tank, the scraper operative for scraping thewall of the tank, and (c) a control system for the elastic scraper,designed and configured to activate the scraper so as to promote thedeposition of scale on the wall.

According to another aspect of the invention, the electrochemical devicefor scale treatment includes: (a) an electrochemical cell having: (i) ametallic tank for receiving a water supply, the tank forming a cathodeof the electrochemical cell, and (ii) at least one anode, disposedwithin the tank; the electrochemical cell being operative to produce apH above 12 near a wall of the tank, so as to form a scale deposition onthe wall, thereby removing the deposition from the water supply; (b) anelastic scraper disposed within the tank, the scraper operative forscraping the wall of the tank, and (c) a control system for the elasticscraper, designed and configured to supply a predetermined constantcurrent for activating the scraper so as to promote the scale depositionon the wall.

According to yet another aspect of the invention, there is provided anelectrochemical method of scale treatment in water supply systems, themethod including the steps of: (a) providing a system having: (i) anelectrochemical cell including: a metallic tank for receiving a watersupply, the tank forming a cathode of the electrochemical cell and ananode, disposed within the tank; (ii) an elastic scraper disposed withinthe tank, the scraper operative for scraping a wall of the tank; (b)operating the cell so as to operatively produce a pH above 12 near thewall of the tank, so as to form a scale precipitate on the wall, therebyremoving the precipitate from the water supply, and (c) controlling anoperation of the scraper so as to promote the scale deposition on thewall.

According to one preferred embodiment of the present invention, theanode includes a material selected from the group consisting ofaluminum, magnesium, and zinc.

According to another feature in the described preferred embodiments, theanode includes an alloy including TiNiO and/or a metal coated by analloy including TiNiO.

According to still another feature of the present invention the controlsystem is an automatic control system having a pneumatic or electricalcontrol mechanism.

According to still another feature of the present invention, the controlsystem includes at least one indicator for triggering the scraper toscrape the wall.

According to yet another feature in the described preferred embodiments,the indicator is for measuring a physical property associated with athickness of the scale deposition.

According to still another feature in the described preferredembodiments of the present invention, the physical property iselectrical resistance, and the control system is responsive to adifferential in the electrical resistance.

According to yet another feature of the present invention, thedifferential in said electrical resistance is a differential of up to 3ohms.

According to still another feature in the described preferredembodiments of the present invention, at least one indicator is designedand configured to trigger the scraper to scrape the wall when the scaledeposition attains a thickness of up to 2 mm.

According to yet another feature in the described preferred embodiments,at least one indicator is designed and configured to trigger the scraperto scrape the wall when the scale deposition attains a thickness of upto 0.5 mm.

According to still another feature in the described preferredembodiments, the control system includes a timing mechanism, designedand configured to trigger said scraper according to a pre-determinedtime parameter.

According to yet another feature of the present invention, thepredetermined time parameter is a fixed time interval.

According to still another feature of the present invention, the fixedtime interval is up to 12 hours.

According to yet another feature in the described preferred embodiments,the fixed time interval is up to 1 hour.

According to still another feature in the described preferredembodiments of the present invention, the electrical power supply isdesigned and configured to supply a pre-determined constant current.

According to yet another feature of the present invention, the elasticscraper includes a circumferential elastic ring for ensuring a closecontact while removing scale by the scraper.

According to still another feature in the described preferredembodiments, the control system is designed and configured to activatethe scraper according to a combined function including the physicalproperty and the pre-determined time parameter, wherein the physicalproperty is preferably the electrical resistance or the electricalconductivity.

According to still another feature of the present invention theelectrochemical method further includes the step of measuring a physicalproperty correlated with a thickness of the scale deposition, to obtaina measurement, wherein the controlling of the scraper operation is atleast partially based on said measurement.

Finally, according to yet another feature in the described preferredembodiments of the present invention, the physical property is selectedfrom the group consisting of electrical resistance and electricalconductivity.

Thus, the present invention successfully addresses the shortcomings ofthe prior art by providing a simple robust and inexpensive improvedmethod of, and device for, electrochemically treating water supplysystems that further reduce the water hardness (i.e., the level ofunprecipitated scale) in such systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings. With specific reference now tothe drawings in detail, it is stressed that the particulars shown are byway of example and for purposes of illustrative discussion of thepreferred embodiments of the present invention only, and are presentedin the cause of providing what is believed to be the most useful andreadily understood description of the principles and conceptual aspectsof the invention. In this regard, no attempt is made to show structuraldetails of the invention in more detail than is necessary for afundamental understanding of the invention, the description taken withthe drawings making apparent to those skilled in the art how the severalforms of the invention may be embodied in practice.

In the drawings:

FIG. 1 is a schematic cross-sectional view of the inventiveelectrochemical device having a scale scraper for removing scale fromwater supply systems.

FIG. 2 is a graph comparing the level of water hardness (expressed asppm of dissolved calcium) attained using: a constant voltage device(device A) of the prior art; a similar device having a scraper of theprior art (device B), and an inventive device (device C) having a novelscraping technology and operating at constant current.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a method of, and device for, electrochemicallytreating water supply systems so as to greatly reduce the water hardnesswith respect to similar, known electrochemical water treatment systems.The inventive device effectively induces scale to precipitate on theinner wall of the water treatment tank.

The principles and operation of the system and method according to thepresent invention may be better understood with reference to thedrawings and the accompanying description.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not limited in its applicationto the details of construction and the arrangement of the components setforth in the following description or illustrated in the drawing. Theinvention is capable of other embodiments or of being practiced orcarried out in various ways. Also, it is to be understood that thephraseology and terminology employed herein is for the purpose ofdescription and should not be regarded as limiting.

In my Israeli Patent No. 120,003 is disclosed a modified Guldager systemhaving non-dissolving electrodes made of, or coated with, a TiNiO alloy.In this system, the scale is deposited on the inner wall of the tank,and is removed by a scraping action against the wall.

Referring now to the drawings, FIG. 1 is a schematic cross-sectionalview of an improved electrochemical device having a scale scraper forremoving scale from water in a water supply system. Electrochemicaldevice 100 includes a cathode-wall 20 of metallic water tank 12, and atleast one, and typically, at least two anodes 10 a and 10 b attached tocover 14, disposed longitudinally in tank 12, and typically extendalmost to the bottom 16 thereof.

According to yet another feature in the described preferred embodiments,Anodes 10 a and 10 b are made of aluminum, or preferably of TiNiO thusenabling the delivery of high electrical currents to the electrochemicalcell, without dissolving anodes 10 a and 10 b and consequently, withoutcontaminating the treated water with undesirable metal ions andcolloidal sludge.

When current is delivered to the electrochemical cell via an electricalpower supply 18, the water close to wall 20 attains high pH values(typically, 12 to 14). Consequently, various dissolved carbonates andmetal oxides in the water within tank 12 precipitate on wall 20. Powersupply 18, which is designed and configured to supply a constantcurrent, preferably supplies a direct current. It should be emphasizedthat in prior art constant voltage devices, the scale layer growthincreases the electrical resistance, consequently reducing theelectrical current and scale deposition rate. In sharp contradiction toconstant voltage devices, constant current operation of electrochemicaldevice 100 enables to deposit scale 24 at a substantially constant, highrate. During the deposition, scale layer growth causes an increase inelectrical resistance, and hence in the voltage required to keepconstant electrical current that ensures constant scale deposition rate.

As disclosed in my Israeli Patent No. 120,003, tank 12 includes ascraper 22 that mechanically cleans and removes scale 24 that isdeposited on wall 20. Scraper 22 consists of a disc 44, typically, butnot necessarily, metallic, designed and configured with adjustableopenings that enable the installment of anodes 10 a and 10 b, and enablefree movement of scraper 22.

Whenever scale cleaning is desired or needed, the water flow is stoppedby closing inlet valve 32, scraper 22 is moved slowly downwards bypiston 28 (installed in a piston housing 30) so as to scrape off scale24 from inner wall 20. When scraper 22 reaches its lowest position,draining valve 26 is opened and the slurry of loose particles and wateris drained out. After draining, water tank 12 is thoroughly rinsed byopening water inlet valve 32, while water outlet valve 34, which is a3-way valve, is diverted to drain the water out of the system untilclear water comes out. After thoroughly rinsing the tank, scraper 22 israised back to its normal position, and outlet valve 34 returns to anormal operating position, such that feed water again flows into thesystem.

Table 1 and FIG. 2 describe a typical experiment that was conducted totest the performance of the present invention in comparison to prior artdevices. In the experiment, feed water was electrochemically treatedusing one of three devices: an ordinary constant voltage device (deviceA), a similar device equipped with a scale scraper (device B), and byelectrochemical device 100 of the present invention. Table 1 records thewater hardness (in ppm ) achieved in these devices during each day ofoperation. Column A relates to device A, Column B to device B, andColumn C to device 100. The measurements given in Table 1 are alsoprovided graphically in FIG. 2 as curves A. B and C, respectively. TABLE1 Water hardness (ppm calcium) in the devices vs. day of operationCalcium Hardness (ppm CaCO₃) Days A B C 1 243 243 243 2 230 218 170 3225 206 110 4 205 170 85 5 228 180 68 6 210 180 52 7 205 170 67 8 220205 51 9 200 175 65 10 225 170 53

It is observed from Table 1 and FIG. 2 that while device A graduallyreduced the water hardness from 243 ppm to 205 ppm over the first 4 daysof operation, no further reduction was achieved thereafter. Device B,which was equipped with a prior-art scraping mechanism (as taught by myIsrael Patent No. 120,003), exhibited an improved scale-precipitatingperformance, reducing the water hardness from 243 ppm to 170 ppm overthe first 4 days of operation. However, no further reduction wasachieved thereafter.

Until recently, the known function of scraper 22 was to periodicallyremove scale 24 from the inner wall 20 of tank 12, so as to prevent anexcessive build-up of scale. In my co-pending, unpublished (and as such,is not to be construed as prior art with regard to the presentapplication) Israeli Patent Application Serial No. 151,181, which isincorporated by reference for all purposes as if fully set forth herein,it is taught that when the thickness of the precipitated salts reachesabout 0.3-0.5 cm, the electrical resistance reaches unacceptably highvalues and scale cleaning is necessary.

Surprisingly, it has been discovered by the inventor that carefulmonitoring and control of the scraping operation for removing scale 24from wall 20 (the cathode of the electrochemical cell) of tank 12greatly increase the rate of scale deposition on the surface of thewall, such that the level of unprecipitated scale in the water beingprocessed is appreciably reduced.

The control scheme is preferably based on a physical parameterassociated with, or correlated to, the depth of crystallized scale 24.

Control system 36 is advantageously installed, along with power supply18, in panel 38. Control system 36 may be an automatic (using, by way ofexample, a pneumatic or electrical mechanism) control system. Variousindicators can be used to trigger the operation of piston 28. Theseindicators may measure electrical resistance or conductivity, whichlargely depend on the depth of crystallized scale 24, etc.

Although the electrical conductivity of water may vary from location tolocation, and from process to process, it has been discovered by theinventor that an increase in electrical resistance of up to 3 ohmsindicates that scraper 22 (by means of piston 28) should be operated toscrape scale 24 from the inner wall 20 of tank 12. Preferably, anincrease in electrical resistance of up to 2 ohms, and more preferably,up to 1 ohm, should be used as a control criterion for activatingscraper 22.

As used herein in the specification and in the claims section thatfollows, the term “differential” or “increase”, with respect toelectrical resistance within the electrochemical cell, refers to thedifference between the electrical resistance at any given time and areference or baseline electrical resistance. Preferably, the referenceelectrical resistance is the electrical resistance after a previousscraping, most preferably the immediately previous scraping.

In another preferred embodiment, control system 36 includes a timer 40(also located in panel 38), for activating scraper 22 based onpre-determined time settings, e.g., at a fixed time interval. The timeinterval between cleaning of inner wall 20 should be less than 12 hours,preferably less than 4 hours, more preferably less than 2 hours, andmost preferably less than around 1 hour.

As used herein in the specification and in the claims section thatfollows, the term “fixed time interval”, with respect to a scrapingoperation, refers to a time interval between two successive scrapings.

It must be emphasized that control systems based both on electricalresistance (or another parameter correlated with scale depositionthickness) and time interval achieve superior results in terms of therate of scale deposition on inner wall 20. Specifically, it has beenfound that by augmenting the electrical resistance criterion with amaximum time elapsed between scrapings criterion greatly improves theperformance.

When the sole criterion for activating the scraper is electricalresistance, I have found that the rate of scale deposition oftendecreases with time. Without wishing to be bound by theory, I attributethis decrease to various surface effects on the crystalline scalesurface, including sliming, which reduce the effective surface area ofscale crystals that is available for enhancing additional scaledeposition. Such surface effects appear to have little effect onelectrical resistance.

Hence, by incorporating an additional criterion—that of maximum timeelapsed between scrapings, the deleterious surface effects on thecrystalline scale surface are curtailed, and the rate of scaledeposition remains substantially constant over time.

In another preferred embodiment of the present invention, scraper 22 ofdevice 100 is equipped with a scale-cropping element for reducing thethickness of the scale deposition on inner wall 20 to a pre-determinedthickness. In FIG. 1, the specific, non-limiting embodiment of thescale-cropping element is circumferential elastic ring 46. Elastic ring46 may be bonded to scraper 22, or may be manufactured as an integralpart of scraper 22. Elastic ring 46 is preferably made of rubber oranother elastomeric material, including, but not limited to, neoprene,butyl rubber and/or butadiene.

Equipped with elastic ring 46, device 100 is capable of removing scale24, such that there remains only a thin layer of scale of up to 2000microns, preferably less than 800 microns, and more preferably less than500 microns. As a result, after each scraping operation, device 100returns to working conditions at which the maximum scale deposition rateis observed.

Referring back to Table 1 and FIG. 2, it is observed that by sharpcontrast to devices A and B of the prior art, device C (device 100 ofFIG. 1) sharply reduces the concentration of dissolved calcium after thefirst 4 days of operation, from an initial concentration of 243 ppm toonly 85 ppm. Moreover, the concentration of dissolved calcium continuesto drop, stabilizing at a level of about 55 ppm over the next six daysof operation.

The concentration of dissolved calcium achieved—55 ppm, is substantiallyand surprisingly lower than the 170 ppm dissolved calcium achieved usinga similar, scraper-equipped unit of the prior art. The inventive deviceattained a reduction in the concentration of dissolved calcium of 77%,which compares quite favorably to the 30% reduction attained using themost similar unit of the prior art.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims. All publications, patents and patentapplications mentioned in this specification are herein incorporated intheir entirety by reference into the specification, to the same extentas if each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present invention.

1. An electrochemical device for scale treatment in water supplysystems, comprising: (a) an electrochemical cell including: (i) ametallic tank for receiving a water supply, said tank forming a cathodeof said electrochemical cell; and (ii) at least one anode, disposedwithin said tank; said electrochemical cell for operatively connectingto an electrical power supply, said electrochemical cell operative toproduce a pH above 12 near a wall of said tank, so as to form a scaledeposition on said wall, thereby removing said deposition from saidwater supply; (b) an elastic scraper disposed within said tank, saidscraper operative for scraping said wall of said tank; and (c) a controlsystem for said elastic scraper, said control system designed andconfigured to activate said scraper so as to promote said scaledeposition on said wall.
 2. The electrochemical device of claim 1,wherein said anode includes a material selected from the groupconsisting of aluminum, magnesium, and zinc.
 3. The electrochemicaldevice of claim 1, wherein said anode includes a material selected fromthe group consisting of an alloy of TiNiO and a metal coated by an alloyof TiNiO.
 4. The electrochemical device of claim 1, wherein said controlsystem is an automatic control system, said automatic control system hasa control mechanism selected from the group consisting of a pneumaticmechanism and an electrical system.
 5. The electrochemical device ofclaim 1, wherein said control system includes at least one indicator,said at least one indicator for triggering said scraper to scrape saidwall.
 6. The electrochemical device of claim 5, wherein said indicatoris for measuring a physical property associated with a thickness of saidscale deposition.
 7. The electrochemical device of claim 6, wherein saidphysical property is electrical resistance, and wherein said controlsystem is designed and configured to activate said scraper responsive toa differential in said electrical resistance.
 8. The electrochemicaldevice of claim 7, wherein said differential in said electricalresistance is a differential of up to 3 ohms.
 9. The electrochemicaldevice of claim 5, wherein said at least one indicator is designed andconfigured to trigger said scraper to scrape said wall when saidthickness of said scale deposition reaches up to 2 mm.
 10. Theelectrochemical device of claim 5, wherein said at least one indicatoris designed and configured to trigger said scraper to scrape said wallwhen said thickness of said scale deposition reaches up to 0.5 mm. 11.The electrochemical device of claim 1, wherein said control systemincludes a timing mechanism, said timing mechanism being designed andconfigured to trigger said scraper according to a predetermined timeparameter.
 12. The electrochemical device of claim 11, wherein saidpre-determined time parameter is a fixed time interval.
 13. Theelectrochemical device of claim 12, wherein said fixed time interval isup to 12 hours.
 14. The electrochemical device of claim 12, wherein saidfixed time interval is up to 1 hour.
 15. The electrochemical device ofclaim 1, wherein said electrical power supply is designed and configuredto supply a pre-determined constant current.
 16. The electrochemicaldevice of claim 1, wherein said elastic scraper includes acircumferential elastic ring, said circumferential ring configured topromote contact between said ring and said scale deposition duringremoval of said scale deposition.
 17. The electrochemical device ofclaim 6, wherein said control system is designed and configured toactivate said scraper according to a combined function including saidphysical property and a pre-determined time parameter.
 18. Anelectrochemical device for scale treatment in water supply systems,comprising: (a) an electrochemical cell including: (i) a metallic tankfor receiving a water supply, said tank forming a cathode of saidelectrochemical cell; and (ii) at least one anode, disposed within saidtank; said electrochemical cell for operatively connecting to anelectrical power supply, said electrochemical cell operative to producea pH above 12 near a wall of said tank, so as to form a scale depositionon said wall, thereby removing said deposition from said water supply;(b) an elastic scraper disposed within said tank, said scraper operativefor scraping said wall of said tank; and (c) a control system for saidelastic scraper, said control system designed and configured to supply apredetermined constant current for activating said scraper so as topromote said scale deposition on said wall.
 19. The electrochemicaldevice of scale treatment of claim 18, wherein said control systemincludes a timing mechanism, said timing mechanism being designed andconfigured to trigger said scraper according to a pre-determined timeparameter.
 20. The electrochemical device of scale treatment of claim19, wherein said pre-determined time parameter is a fixed time interval.21. An electrochemical method of scale treatment in water supplysystems, the method comprising the steps of: (a) providing a systemincluding: (i) an electrochemical cell including: (I) a metallic tankfor receiving a water supply, said tank forming a cathode of saidelectrochemical cell; and (II) at least one anode, disposed within saidtank; (ii) an elastic scraper disposed within said tank, said scraperoperative for scraping a wall of said tank; (b) operating said cell soas to operatively produce a pH above 12 near said wall of said tank, soas to form a scale precipitate on said wall, thereby removing saidprecipitate from said water supply; and (c) controlling an operation ofsaid scraper so as to promote said scale deposition on said wall. 22.The electrochemical method of scale treatment of claim 21, furthercomprising the step of: (d) measuring a physical property correlatedwith a thickness of said scale deposition, to obtain a measurement,wherein said controlling of said operation of said scraper is at leastpartially based on said measurement.
 23. The electrochemical method ofscale treatment of claim 22, wherein said physical property is selectedfrom the group consisting of electrical resistance and electricalconductivity.